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Home , Halite, Khewra Salt Mine, Mineral lick, Salt Range, Salt tectonics

Journal of Asian Earth Sciences 113 (2015) 922–934

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Journal of Asian Earth Sciences

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Macrostructures vs microstructures in detachments: An example from the Range, ⇑ L. Richards a, , R.C. King a, A.S. Collins a, M. Sayab b, M.A. Khan c, M. Haneef d, C.K. Morley e, J. Warren f a Centre for Resources and Exploration (TRaX), Department of Earth Sciences, University of Adelaide, Adelaide 5005, South , Australia b Geological Survey of Finland, P.O. Box 96, FI-02151 Espoo, Finland c Karakoram International University, University Road, Gilgit, Gilgit-Baltistan, Pakistan d Department of , University of Peshawar, Jamrud Road, , Pakistan e PTTEP, 27th Floor, ENCO Building, Soi 11, Vibhavadi-Rangsit Road, Chatuchak, Bangkok 10900, Thailand f Chevron PTTEP International Master Program in Geosciences, Room # 239a, Department of Geology, Faculty of Science, Chulalongkorn University, 254 Phyathai Rd., Patumwan, Bangkok 10300, Thailand article info abstract

Article history: The , Pakistan is the surface expression of an evaporite detachment over which the Potwar Received 22 January 2015 Plateau fold-thrust belt has moved. Whilst previous publications regarding this region have focused on Received in revised form 31 March 2015 the petroleum prospectivity, deformation, and large-scale processes, this paper characterises the Salt Accepted 2 April 2015 Range detachment at the meso-(10 cm to 10s of metres) and micro-scale (cm to lm) and examines cor- Available online 24 April 2015 relations to the macro-scale (10s of metres to kms). Two detailed scaled cross sections are analysed alongside structural measurements to characterise the detachment at the meso-scale with optical anal- Keywords: ysis of microstructures that formed during deformation characterising the micro-scale. Both ductile and Salt Range brittle features observed in cross section indicate composite deformation processes acting simultane- Pakistan Evaporite detachment ously; this contrasts with models of salt detachments behaving homogeneously. Microstructural analysis Microstructures indicates processes of grain boundary migration and lattice distortions. The microstructurally Fold-thrust belt revealed competition between intra-crystalline deformation and recrystallization at shallow depths and low temperatures links passes up-scale to mesoscale evaporite mylonites and progressively in the weaker units, whereas more brittle processes operate in the stronger lithologies in this near-unique out- crop of a the emergent toe of a major salt-bearing detachment fault. Ó 2015 Elsevier Ltd. All rights reserved.

1. Introduction Morley and Guerin, 1996; Rowan et al., 2004). The style of defor- mation within fold-thrust belts is strongly influenced by the nature Shortening of the Earth’s crust is commonly accommodated by of the detachment, such as strength of the overlying strata, lithol- fold-thrust belts that are mechanically decoupled from the under- ogy, pore-pressure, coefficient of friction, dip and dip direction of lying rocks by a detachment zone or horizon (Dahlstrom, 1969; the detachment (Davis et al., 1983; Jaumé and Lillie, 1988; Davis et al., 1983). The creation of fold-thrust belts is typically Dahlstrom, 1990; Koyi and Vendeville, 2003; Suppe, 2007; the result of far-field stresses, near-field stresses, or a combination Simpson, 2010). of both (e.g. King et al., 2010; King and Backé, 2010; Morley et al., The South Potwar Basin, Pakistan, is an example of a distal fore- 2011b). The driving force of deformation defines whether the land fold-thrust belt detaching over a thick salt layer, the Salt fold-thrust belt is thin-skinned, internally driven deformation, or Range Formation (Krishnan, 1966; Jaumé and Lillie, 1988; Jaswal thick-skinned where far-field stresses are dominant; a combina- et al., 1997). The fold-thrust belt is being driven by a combination tion of both is possible depending on the nature and number of of far-field stresses (continent–continent collision) and near-field active detachment layers (Morley and Guerin, 1996; King et al., stresses (gravity gliding) (Jaumé and Lillie, 1988; Davis and Lillie, 2010; Morley et al., 2011b). Detachments are typically units of 1994) and represents the southernmost expression of the overpressured shale or salt and it is the extent of these units that Himalayan orogenic deformation (Jaumé and Lillie, 1988; Davis determines the area of related deformation (Dahlstrom, 1990; and Lillie, 1994; Grelaud et al., 2002). of the Potwar Plateau are transported aseismically over the 2 ± 1° northward dip- ⇑ Corresponding author. Tel.: +61 8 8313 4971. ping basement, though local asperities within the detachment E-mail address: [email protected] (L. Richards). facilitate some seismic activity (Davis and Lillie, 1994; Satyabala http://dx.doi.org/10.1016/j.jseaes.2015.04.015 1367-9120/Ó 2015 Elsevier Ltd. All rights reserved. L. Richards et al. / Journal of Asian Earth Sciences 113 (2015) 922–934 923 et al., 2012). A down-to-the-north, normal, basement fault Here, we present structural observations and cross-sections within observed in seismic section (lines CW-13 and KK-4) causes the the Salt Range Formation and use these to characterise the Salt Range Thrust to propagate to the surface forming the epony- meso-scale structure of the detachment. Samples taken along these mous Salt Range (Fig. 1C) (Lillie et al., 1987; Baker et al., 1988). cross-sections were analysed using an optical microscope to char- Buttressing of the southward-moving allochthonous Potwar acterise the microstructural features of the detachment. We then Plateau against this fault accumulated stress at the site of this discuss the meso- and micro-scale control on the larger-scale basement fault (Davis and Lillie, 1994; Cotton and Koyi, 2000). fold-thrust belt geometry. The increased stress, distal loading, and salt lubricated faulting resulted in thrusting of the Neoproterozoic to Eocene rocks comprising The Salt Range above Quaternary sediments of the 2. Geological setting Plain (Fig. 1D) (Jaswal et al., 1997; Yeats et al., 1984). Analyses of fold-thrust belts are extensively documented at the 2.1. Regional setting macro-scale (10’s of kms), in the form of regional cross-sections, seismic interpretation, satellite data, and physical and numerical The Salt Range exposes Neoproterozoic to Eocene sedimentary modelling (Lillie et al., 1987; Dirkzwager and Dooley, 2008; Chen rocks of the Salt Range, , Nilawahan, and Chharat Groups and Khan, 2009; King et al., 2010; Morley et al., 2011b); yet few up to the Eocene Limestone Formation, which forms the have attempted to explore the detailed structure of detachments highest peak (Fig. 1D). The interior and direct hanging-wall of at outcrop or smaller scale (e.g. Hansberry et al., 2014). Studying the Salt Range Thrust is composed of the Neoproterozoic Salt detachments at outcrop scale presents a number of difficulties; Range Formation, which forms the detachment underlying the the majority of currently active detachments occur in inaccessible associated fold-thrust belt to the north. This detachment is respon- submarine settings, whilst the few active subaerial fold-thrust sible for the observed thin-skinned contractional wedge geometry belts have insufficient degrees of erosion to allow surface outcrop in the fold-thrust belt (Lillie et al., 1987). On a larger scale, the Salt of the detachment (Hansberry et al., 2014). Our recent fieldwork, Range mirrors the geometry of the Himalayan Orogen displaying a carried out in the area of Khewra, Pakistan, has focused on the roughly E-W trend as it is a distal structure of the same orogenic structures within the Salt Range Detachment (Fig. 1A and B). event.

Fig. 1. Location map, cross section, column. (A) Location map of the study area. (B) Geological map of the eastern Salt Range and Potwar Plateau. The dashed line AB indicates the approximate transect of the cross section in (C). MBT = Main Boundary Thrust, NPDZ = North Potwar Deformation Zone, KMF = Khari Murat Fault, SB = Soan Backthrust, SS = Soan Syncline, RF = Riwat Fault, DT = Domeli Thrust, SRT = Salt Range Thrust (after Kovalevych et al., 2006). (C) Cross section through the NPDZ, SS, and Salt Range showing imbricate stacking, pop-up and/or pop-down structures, and a thickened zone of salt above a basement fault, respectively (after Cotton and Koyi, 2000). (D) Stratigraphic column of the units within the study area (after Grelaud et al., 2002). (E) Salt Range Member subdivisions (After Sameeni, 2009 and Ghazi et al., 2012). 924 L. Richards et al. / Journal of Asian Earth Sciences 113 (2015) 922–934

2.2. Stratigraphy The presence of the Salt Range Formation has accom- modated the southward transport of the Potwar Plateau almost The stratigraphy can be segregated into four major, mechanical aseismically, while maintaining an extremely narrow and lithostratigraphic, units (Fig. 1D) (Khan et al., 1986; Grelaud cross-sectional taper (Davis and Lillie, 1994; Satyabala et al., et al., 2002). 2012). Jaumé and Lillie (1988) suggested that the northern The oldest unit is the Precambrian crystalline basement of the Potwar Plateau was initially a relatively high-angle (1.7°) taper Indian plate that crops out 80 km south of the Salt Range in the fold-thrust belt caused by frictional sliding on a non-salt lithology (Gee, 1989). It is thought to be exposed as the current prior to 2 Ma. Transposition over the salt basin halted the intense forebulge created through loading of the Himalayas on the Indian deformation thus eliminating the necessity of the large taper. Plate (Yeats and Lawrence, 1984; Lillie and Yousuf, 1986; Duroy Subsequent erosion resulted in the present-day low-angle taper et al., 1989). and topography. Deformation within the Salt Range occurred at Ediacaran to early Cambrian evaporites of the Salt Range 5 Ma and again at 2 Ma, the hiatus between these two stages is Formation overlie this basement and form the structural detach- believed to be caused by break-back thrusting on the northern ment (Jaumé and Lillie, 1988; Grelaud et al., 2002). This unit con- limb of the Soan Syncline (Lillie et al., 1987; Burbank and Beck, sists of a crystalline base intercalated with and 1989). Recent earthquakes within the Kohat Plateau, to the overlain by gypsiferous marl, which is covered by –dolo- north-west, and the Potwar Plateau indicate that the detachment mite with infrequent seams of oil shale (Ghazi et al., 2012). may still be currently active. These earthquakes occur where the Lying above the Salt Range Formation are Cambrian to Eocene salt detachment has evacuated and a highly frictional weld of cara- platform deposits that vary between 200 and 500 m thick. The pace sediments lies directly on basement, focusing stress Cambrian and Permian deposits of the Jhelum and Nilawahan (Satyabala et al., 2012). Groups comprise red, maroon and purple , siltstones, and shale, which are overlain by Late Permian to Eocene fossilifer- 3. Methodology ous carbonates (Ghazi et al., 2012). Mechanically the Jhelum and Nilawahan Groups are often referred to as one homogenous ‘cara- 3.1. Structural data pace’ as they decouple above the evaporite detachment with little internal deformation (Butler et al., 1987; Lillie et al., 1987). The During our recent field season in the Salt Range two youngest unit is separated from the underlying stratigraphy by a cross-sections were completed. The first section was taken from non-depositional Oligocene unconformity (Grelaud et al., 2002). a sidewall within the working on the CH22 drive. It is a 6 km thick Miocene to Quaternary age syn-orogenic deposit (Fig. 2) The Billianwala Salt Member (Fig. 1E), which comprises of the and Siwalik Groups that formed from the simul- crystalline halite rock salt with banded layers of marl and potash, taneous uplift and erosion during the Himalayan Orogeny. forms the entirety of the mine and is the main detachment horizon (Butler et al., 1987; Leathers, 1987; Jaumé and Lillie, 1988; Grelaud 2.3. Structural history et al., 2002). This section was chosen due to the quality of exposure and features displayed along it. The cross-section is 25 m long and From south to north, the region comprises the Salt Range, South trends N-S bending slightly in the southern end to a NE–SW trend Potwar Basin, Soan Syncline, and North Potwar Deformation Zone (Fig. 3). The second cross-section was taken through a road cutting (Fig. 1B). The North Potwar Deformation Zone is bound to the north on Khewra Road, 3.5 km north of the town of Khewra. This road by the Main Boundary Thrust and is characterised by imbricate cutting displays a large continuous outcrop of gypsiferous marl duplexing in the footwall of the Main Boundary Thrusts (Cotton of the Sahwal Marl Member with numerous inclusions of blocky and Koyi, 2000). Abutting the North Potwar Deformation Zone to and sheared gypsum from the Bandarkas Gypsum Member the south is the Soan Syncline’s northern limb hosting the Soan (Fig. 1E). This cross-section also trends N-S and measures 110 m Backthrust. This northern limb is upturned forming a monocline in length. As the primary transport direction of the Salt Range is while further south and into the South Potwar Basin salt cored towards the south, exposures trending N-S are ideal for observa- and pop-up structures occur (Fig. 1B and C) (Cotton tion and analysis of their true geometry. and Koyi, 2000). The significant deformation style difference Detailed scaled diagrams were made displaying the meso-scale between the North Potwar Deformation Zone, Soan Syncline, and bedding and foliation. Other structural features were encountered South Potwar Basin is due to the presence of the Salt Range including duplexes, folds, fractures, and shear planes. Structural Formation evaporite detachment (Lillie et al., 1987). The Salt measurements were recorded at known (measured) locations for Range itself results from southwards movement of the Potwar all structural features and bedding where possible. Plateau being buttressed by an E-W striking, down to the north basement normal fault. The southward movement and thickening 3.2. Sample preparation and methodology of the Salt Range Formation beneath the hanging wall is attributed to salt withdrawal and migration instigated by differential loading Thin sections were created from five samples taken from the by prograding basin fill and deformation front (Cotton and Koyi, Salt Range, Pakistan (Table. 1). Thin sections were prepared using 2000). The accumulated stress and continued southward progres- the methods laid out in Urai et al. (1985). Sample SRLR-05 was pre- sion, combined with the basement fault, caused internal imbrica- pared unoriented as its coarsely crystalline structure displayed no tion of the detachment and ramping of the Salt Range Thrust, discernible fabric. Two blocks cut from sample SRLR-06 were pre- which accommodate approximately 25–30 km of shortening pared: one, along the X–Z plane and two, along the Y–Z plane, (Baker et al., 1988; Cotton, 1997; Cotton and Koyi, 2000). The pres- where X–Y is the foliation plane. Samples were cut into appropri- ence of Neoproterozoic to early Cambrian gypsiferous deposits ately sized blocks and adhering to glass slides with araldite epoxy within the Hazara District, north of the MBT, combined with the before being ground and lightly polished with kerosene as a lubri- coeval similarly restricted marine deposits in southern Oman, cant. The samples were then chemically etched in a slightly under-

Iran, and northwest India suggest widespread evaporite deposition saturated (5.5 M) NaCl solution containing 0.8 wt% FeCl36H2O. across the area (Lillie et al., 1987; Kovalevych et al., 2006; Smith, After 40 s this etchant was removed by a powerful stream of kero- 2012). sene and the specimen immediately dried using hot air. L. Richards et al. / Journal of Asian Earth Sciences 113 (2015) 922–934 925

Fig. 2. Mine map. A map showing the workings and distribution of informal sub-units of the Salt Range Formation inside the Khewra Mine. The mine tunnels represent east- west running mine drives intersecting the north-south oriented drives and cavities represented on this map.

Fig. 3. Mine cross section. A detailed scaled cross-section through the Salt Range, Billianwala Salt Member above a composite panorama photo section of the Khewra Mine wall exposure. A–F Indicate locations of detailed feature photos (Fig. 4).

The mechanical polishing stage caused a significant issue in that 4.1. Cross sections inclusion of much harder formed resistant nodules on the slide surface as they are far more resistant to mechanical wear than Two structural cross-sections were made during recent field- the surrounding halite. These nodules would often break away work to Khewra, Pakistan (Fig. 1B). The map of the Khewra Mine, leaving long scours or gouges in the polished halite surface. The below, presents a north to south cross-sectional view of the mine’s later etching stage significantly reduced the appearance of these, distribution of informal sub-units and workings (Fig. 2). although some are still visible. 4.1.1. Section 1: Khewra salt mine section This cross section was constructed from structural measure- 4. Results ments, scaled diagrams, and photos taken within the working Khewra Salt Mine (Fig. 3) along the N-S running mine drive The results presented here were collected and analysed with CH22. The section roughly crosscuts the bedding and foliation classic structural techniques in the form of cross sections and opti- trend. A strong foliation parallel to lithological boundaries may cal microscopy. The locations for each cross section and all samples represent highly transposed primary bedding though no unam- taken are presented along with descriptions and analyses for each biguous primary bedding features could be identified. Bedding (Table. 1). generally dips to the NW in the Khewra region, which is concurrent 926 L. Richards et al. / Journal of Asian Earth Sciences 113 (2015) 922–934

Table 1 Sample analysis table. This table lists the samples and provides specific details including locations, descriptions, and analyses conducted for each.

Sample Location Description Optical analysis

SRLR-01 Khewra Gorge Wavy laminar opaque gypsum of the Bandarkas Gypsum Member. SRLR-02N32° 390 48.300 Black organic rich shale SRLR-03E73° 000 17.200 Laminar opaque gypsum forming part of a fold SRLR-04 Sawal Village Coherent large blocky gypsum with weathered surface grooves U N32° 390 2300 E73° 000 17.200 SRLR-05 Khewra Mine White and clear very coarsely crystalline halite with minor orange potash marl inclusions U SRLR-06N32°38052.800 Coarsely crystalline halite with large bands and inclusions of red maroon potash marl U E73°00030.200 Specific locations in Fig. 3 SRLR-07 Khewra road cutting White and grey micro-crystalline gypsum from a large foliated block U SRLR-08N32°38055.400 Thin wavy slivers of fibrous selenite in red marl SRLR-09E72°59037.800 Gypsum cataclasite with angular fragments of gypsum in red marl matrix U SRLR-10to Foliated gypsum slivers staked like plates with small amounts of red marl N32°38052.500 E72°59040.000 Specific locations in Fig. 6

with the foliation dip-data collected (mean dip/dip direction of sub-section 3). Between 19 m and 23 m there is another potash 44/348). marl layer though it is purer with fewer and smaller halite boudins The southern end of the section begins in an orange and white (Fig. 3 sub-section 4). The remainder of the section returns pre- layered halite that, from 10 m, sharply transitions into a layer of dominantly to orange and white halite. Between 13 m and 17 m maroon-coloured potash marl containing relatively competent blast fractures are clearly visible. halite boudins (Fig. 3, sub-sections 1 & 2), which the foliation anas- Within the large halite layers very few structures are visible tomoses around (Fig. 4B and D). This changes at 17 m to a 2 m aside from the layering (Fig. 4A). This layering is compositional thick, pink to red, massive coarsely crystalline halite layer (Fig. 3 with red and orange layers comprising salts and clay

Fig. 4. Mine feature photos. A collection of detailed photos displaying specific features from the Khewra Mine cross-section (Fig. 3). (A) White halite with orange potash marl inclusions forming layers. (B) Boudins of clear and white halite in halite and potash marl. (C) Large multicrystalline boudins of halite and potash within a potash marl layer adjacent to a large layer of clear and white coarsely crystalline halite. (D) Larger scale photo of Fig. 3B displaying the anastomosing nature of the potash marl layers. (E) Halite boudins in potash marl indicating sense of movement and textural variation. (F) Massive white halite with thin potash marl layers. L. Richards et al. / Journal of Asian Earth Sciences 113 (2015) 922–934 927 minerals. Some of the white halite is completely transparent, form- ing glass-like parts of the outcrop. The potash layers range in col- our from a deep maroon to a light salmon pink. Hand specimen and thin section petrography with energy dispersive spectrometry (EDS) has revealed that , halite, gypsum, and clay miner- als are present in varying amounts. A study by Kovalevych et al.

(2006) has found polyhalite, (2CaSO4MgSO4K2SO4H2O), halite (NaCl), gypsum (CaSO42H2O), and clay minerals are present in varying amounts. The same study also found

(4MgSO44KCl11H2O), leonite (MgSO4K2SO44H2O), and (MgSO4H2O) within salt samples from the same mine. Notably, all the documented potassic minerals in the Khewra Mine are hydrated, with high levels of sulphate, unlike the syl- vite or that typified, original potash precipitates in marine-derived Cambrian (Warren, 2006).

(CaSO4), which is the sulphate phase in the deeper subsur- face equivalents, has been telogenetically rehydrated to gypsum in both the mine and the road sections. Macroscopically, hydration recrystallisation textures are interlaced with the textures of syn- tectonic deformation. The asymmetric lozenge shape and orienta- tion of the halite boudins indicates a top-to-south non-coaxial shear component movement along the foliation (Fig. 4E). The transposed bedding/shear foliation in this cross-section have a consistent dip and dip direction with a mean orientation of 44/348. With the exception of a few outliers, the pole to plane density is focused in the lower right quadrant (Fig. 5A). The rose diagram presents the orientation trend of the bedding/shear folia- tion measurements (Fig. 5B). The extremely divergent poles of the measurements are due to blast fractures formed during excavation (Figs. 5A and 3).

4.1.2. Section 2: Khewra road section Constructed from structural measurements, detailed scaled sketches, and photos taken from a road cutting on the Khewra Road 3.5 km north of the town of Khewra, this cross section tran- sects through the Sahwal Marl Member that makes up, almost exclusively, the entire outcrop of the Salt Range Formation within the Salt Range mountains (Fig. 6). From end-to-end the section is composed of red gypsum marl with steeply dipping white gypsum mylonites. Compositionally the gypsiferous marl varies from roughly 70–90% gypsum. A strong S–C fabric is evident throughout the outcrop and is visible wherever slivers of gypsum are present. These slivers are 1–3 cm thick and form plate-like sheets in cross section continuing along strike into the outcrop, tapering at their margins (Fig. 7E). Internally, these gypsum sheets preserve fine, sub-mm-scale, foliation planes. On a larger scale the marl is cut by grey gypsum-rich cataclasites, some of which are sheared (Fig. 7A and B). Coherent, deformed, gypsum clasts also occur within the marl, the shape of which may reflect its precursor nodu- lar diagenetic formation (Fig. 7C). Isolated white gypsum slivers will occasionally appear in large homogeneous sections of the red marl. Larger blocks of white gypsum are distinctly visible, often they are foliated and occasionally lineated with slicken lines show- ing a top-to-south sense of movement (Fig. 6). With the exception of the solid coherent blocks of gypsum, the entire outcrop is friable and breaks easily when handled. Fig. 5. Mine Stereonets. Equal-area lower hemisphere stereographic projections of structural measurements taken from the Khewra Mine. (A) Contoured Stereonet The shear fabrics are the most notable structural features pre- displaying bedding and foliation, shear plane, and fracture measurements. (B) Rose sent throughout the Khewra Road section, though extremely well diagram of the same measurements. exposed on the southern end (Fig. 6). Discrete low angle thrusts cut the steeply foliated gypsum mylonites, between 0 m and 7 m, creating a classic S–C fabric with a top-to-south sense of move- (Fig. 8A and B), with the shear planes being consistently shallower ment (Fig. 7D). dipping than the foliation, consistent with the S–C relationship. Equal-area lower hemisphere stereographic projections of ori- Some shear planes plot in the NW quadrant. Fracture measure- entation measurements taken here show a distinct trend, the ments show a more varied spread, plotting consistently in the pole-to-plane density profiles for both foliation and shear planes top NW quadrant though some also plot in the S and SW. the foli- show strong correlation demonstrating moderate to steep NW dips ation dip directions displayed on the rose diagram show a mean 928 L. Richards et al. / Journal of Asian Earth Sciences 113 (2015) 922–934

Fig. 6. Road cross section. A detailed scaled cross-section from a road cutting outcrop through the Salt Range, Sahwal Marl and Bandarkas Gypsum Members abovea composite panorama photo section of the road cutting outcrop exposure. A–E Indicate locations of detailed feature photos (Fig. 7).

Fig. 7. Road feature photos. A collection of detailed photos displaying specific features from the Khewra Road cutting outcrop (Fig. 6). (A) Gypsum cataclasite in Sahwal Marl. (B) Sheared elongate translucent gypsum clasts in gypsum rich cataclasite. (C) Lenses and blocky clasts of gypsum in red marl. (D) S–C fabric in red gypsum marl with numerous gypsum slivers. (E) Sheared gypsum slivers defining the foliation in the red gypsum marl. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.) orientation of 352° (Fig. 8D); this aligns well with the rose diagram 4.2. Microscopic analysis of transposed bedding/shear foliation measurements taken from the Khewra Mine cross-section of 348° and indicates a widespread Five samples underwent optical analysis: three samples, similarity in the observed structures (Fig. 5B). SRLR-04, -07 and -09, from different locations were composed of L. Richards et al. / Journal of Asian Earth Sciences 113 (2015) 922–934 929

Fig. 8. Road Stereonets. Equal-area lower hemisphere stereographic projections of structural (bedding and foliation, shear planes, fractures) measurements taken from the road cutting on Khewra road. (A) Bedding and foliation contoured stereonet. (B) Shear plane contoured stereonet. (C) Fracture contoured stereonet. (D) Rose diagram of the same measurements. gypsum, the other two samples, SRLR-05 and -06, came from deformation (Fig. 9E and F). The chaotic nature of the samples is within the Khewra Mine and are both composed of halite. The further expressed in photomicrographs which show the random aforementioned samples SRLR-04 and -07 are predominantly fea- orientation of veins and comprehensive amalgam of clay and gyp- tureless being entirely composed of gypsum microspar with few sum (Fig. 9G and H). Having been taken from within a gypsum marl inclusions. Sample SRLR-09 shows remarkably different features cataclasite the significant brittle deformation observed is expected, within the same sample. Containing approximately 40% impurities, this also demonstrates the retention of deformation structures the marl is easily distinguishable by the red/white colour contrast within the meso-scale brittle components of the detachment. (Fig. 9B and C). Large grains of pure gypsum microspar interstitial Sample SRLR-05 was taken from the massive crystalline halite with more gritty gypsum are selvedged by red clay (Fig. 9B) is in layer whilst sample SRLR-06 came from a potash marl-rich layer stark juxtaposition with the strongly deformed and apparently to allow for a comparison between the two (Fig. 3). Thin sections chaotic substructure not visible in the purer samples (Fig. 9C). made from sample SRLR-05 showed smaller, 1–5 mm, and a few Small inclusions of organic matter are also present and likely much larger, 0.5–2 cm, subhedral halite (Fig. 9A and D). sourced from the rare oil shale seams after assimilation during The larger crystals demonstrated typical cubic in the form 930 L. Richards et al. / Journal of Asian Earth Sciences 113 (2015) 922–934

Fig. 9. Thin section compilation 1. Thin section photos and photomicrographs of samples SRLR-05 and 09. (A) Thin section of SRLR-05 showing size and distribution of halite grains. (B) Thin section of SRLR-09 displaying a large grain of gypsum microspar (GYP) interstitial with more gritty gypsum (GG) selvedged by red clay (RC). (C) Thin section of SRLR-09 displaying strongly deformed and apparently chaotic substructure. (D) Subset of (A), photomicrograph showing cleavage misorientation, grain boundary morphology and texture of halite in Plane polarised light. (E and F) Subset of (B), photomicrograph displaying a grain of gypsum microspar selvedged by clay with organic matter inclusions (O) in plane polarised, E, and cross polarised light, F. (G and H) Subset of (C), photomicrograph displaying strongly deformed chaotic structure in gypsum marl in plane polarised, G, and cross polarised light, H. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

of large black lines forming distinct orthogonal steps. Many of the acted as a nucleation point for later recrystallisation, likely related large and medium sized grains share smooth gently curving or to thrust related uplift and telogenesis (Holliday, 1970; Artieda, lobate boundaries sometimes with films between which 2013; Moragas et al., 2013). are interpreted to be a result of significant grain boundary migra- tion. In sections where many medium–large grains are in close proximity the cleavage observed in each grain is oriented very dif- 5. Discussion ferently, which is a strong indication that the crystallographic ori- entation is similarly different, at least in the plane of the thin 5.1. Structural significance section (Fig. 9D). Such strong misorientation paired with rounded grain boundaries and the well interlocked nature of the grains Whilst previous work and more recent works have focused on lends heavily to the interpretation that major recrystallisation large km scale sections through the entire stratigraphy (e.g. Gee, occurred after period of significant deformation. 1980; Lillie et al., 1987), the sections presented here focus specifi- Sample SRLR-06 displayed a varied range of features including cally on the detachment zone of the Salt Range from regional to transitioning halite grain sizes, inclusions of gypsum pseudomor- micro scales. The structural measurements presented in Figs. 5 phed after anhydrite, and clay material (Fig. 10). Sample SRLR-06 and 8 are internally consistent and also correlate with the regional contains predominantly halite with some gypsum, potash salts, scale dip direction established in the literature (Lillie et al., 1987; and clay minerals. This sample displays massive recrystallised Cotton and Koyi, 2000). The average dip of foliation (48°), however, halite grains exhibiting cubic cleavage though orthogonal steps is steeper than that usually associated with thrust faults. This over- allude to crystal lattice distortions (Fig. 10A). Aside from these steepening may be due to the ramping of the detachment over the massive grains, the remainder of the halite crystals in the sample basement normal fault. Alternatively, it may result from internal form smaller sub-angular to rounded grains between 50 and back-rotation of the detachment foliation due to 500 lm with brine films, and inclusions, along boundaries forward-propagation duplex-like imbrication, similar to that seen (Fig. 9B). A mass of gypsum crystals, forming in laths or as aggre- in ‘standard’ brittle thrusts (Boyer and Elliott, 1982). Although foli- gates, in a clay matrix is typically found separating these different ation does not necessarily form parallel to the thrust, the distance (Fig. 10A and D). Alternatively, the gypsum laths form over which this deformation has occurred and the ductile nature of wholly within larger coherent halite crystals without any clay salt over geological time commonly results in parallel alignment. (Fig. 10B, D, and E). The gypsum laths also form a felt texture; this The detachment boundary with the units above is parallel and con- and their lath shaped crystals indicate likely alteration after anhy- formable, yet the anastomosing fabric planes and intra-fabric drite (Fig. 10D and E) (Warren, 2006). The clay material masses are asymmetric sigma clasts also demonstrate that the fabric formed interpreted to have behaved as aquifers hosting percolating fluids by non-coaxial shear. The nature of is extremely that further aided in the recrystallisation process and potentially ductile due to the inherent weakness of halite. However, the L. Richards et al. / Journal of Asian Earth Sciences 113 (2015) 922–934 931

Fig. 10. Thin section compilation 2. Photomicrographs taken from thin sections 6A (A and B) and 6B (C–E) in plane polarised light made from sample SRLR-06. Sections 6A display features in the Y–Z plane and 6B display features in the X–Z plane. (A) Massive recrystallised halite grain (HL) showing typical cubic cleavage with some lattice distortions adjacent to clay material (CM) and smaller halite grains. (B) Large halite grain with gypsum intergrowths surrounded by much smaller sub-rounded halite grains. (C) Large recrystallised halite grain transitioning into smaller sub-rounded and elongate grains. (D) Large recrystallised halite grain with gypsum lath (GL) inclusions bounded by clay material, surrounded again by smaller halite grains. (E) Plane polarised (left) and cross polarised (right) photomicrographs showing a completely recrystallised halite grain with gypsum laths and aggregates (GA). presence of boudins within the first cross-section and cataclasites stark contrast to the precursors ( and possibly carnallite demonstrate that the mixed evaporitic provokes a altered to sylvite with burial) that first precipitated from much more complicated rheology between relatively brittle and marine-derived brines in the Cambrian evaporite basin (Smith, ductile minerals and possibly zones, especially if water contents 2012). Inclusion temperatures in coarsely crystalline halites are varied within the salt mass. known to have been reset to lower values during exhumation of The rheological heterogeneity is a likely response to differing the Salt Range halite in the Lesser Himalayan thrust in the nearby levels of evaporite , which occur in the various region. Yet the interlayered dolomite beds and clays pre- halite bearing layers in the Khewra Mine; mineralogical variation serve inclusion and mineralogical evidence of higher burial tem- across unit to unit in the mine will act to control relative perme- peratures (Singh and Singh, 2010). This again illustrates the ability and recrystallisation intensity in both the mesogenetic preferential entry of active phreatic waters into the more soluble and telogenetic realms (Warren, 2006; Moragas et al., 2013). In salt layers during telogenesis. Textures in the rims of the coarsely addition to grain size reduction during deformation, recovery of crystalline halites in the Khewra mine section are defined by sel- euhedral crystal textures in the mine section is tied to the varying vages clay and gypsum, implying that the salt crystals are the as deformed strata are uplifted and pass from the result of growth into a stressed accommodation space, possibly mesogenetic realm into the telogenetic realm. The telogenetic related to a time typified by cross-flows of relatively undersatu- realm is where the deformed and thrusted sedimentary rocks enter rated waters. The combination of micro- and meso-scale structure the zone of renewed active phreatic water crossflows. Our inter- demonstrates the synchronicity of deformation and brine induced pretation of resetting of at least some portion of the halite crystal recrystallisation and recovery (Figs. 4, 7, 9 and 10). parameters is reinforced by the of the various potash The road cross-section illustrates the diversity of deformational minerals now present in the salt mine. All of the current potash features present in this poly-mineralic evaporitic succession mineral assemblages (polyhalite, kainite, leonite and kieserite) in (Fig. 6). Notably, all gypsum now seen in outcrop is derived from the Khewra Mine are hydrated and enriched in MgSO4. This is in anhydrite in the subsurface (Holliday, 1970). The S–C fabric in 932 L. Richards et al. / Journal of Asian Earth Sciences 113 (2015) 922–934 the road section is indicative of a combined brittle–ductile rheol- are interpreted to result from post deformational crystal recovery. ogy. Thin slivers of mm-spaced foliated sheared gypsum dis- Coarsely crystalline halite displays a range of grain sizes. One inter- tributed within the Sahwal Marl pick out the steep fabric in the pretation is that coarser halite crystals represent a progressive foliated domains between the discrete shallow-dipping shear assimilation of small grains into larger ones, leading eventually planes (Fig. 7D and E). However, in contrast to ‘classic’ S–C fabrics to complete recrystallisation into coarsely crystalline halite (Berthé et al., 1979), the ‘S’ planes do not appear to be pure-shear (Figs. 9A, D and 10A). Such textures would then be analogous to features as, locally, the fabric has a pronounced mineral-aggregate the experimental observations of Park and Means (1996). lineation and preserves asymmetric clasts that suggest a However, the consistent sharp boundary to coarse crystalline top-to-the-south simple shear component. The localised shearing halite ocelli and layers, a lack of transitional crystal remnants at during deformation led to the orientation and stretching of the the boundaries of the coarse halite crystals, and the consistent gypsum into the current mylonite slivers. The presence of the cat- association with a clayey, gypsum selvage, argues that the coarse aclasites provides a change in style from ductile to brittle deforma- halite crystals are a response to crossflows of dense telogenetic bri- tion, interpreted to be due to exhumation of the detachment by nes percolating downward along the thrust stratigraphy as halite frontal erosion and the entry of the total succession into a diage- was dissolving shallower in the thrust. The creation of a dense netic environment where anhydrite is altering to gypsum and sig- halite-saturated brine plume moving into a stress induced void, nificant volumes of halite are being leached and remobilised by created during phreatic crossflow is typical of evaporite units crossflows of phreatic water. beginning to experience hypogene karstification (Warren, 2006). This brittle change shares a link to the large (metre to The presence of halite stalactites and stalagmites in some sections decametre-scale) clasts of foliated gypsum. These clasts either of the mine clearly shows that, at least today, halite-saturated formed isolated, or thin, gypsum/anhydrite interbeds in the marl waters are migrating through the mine geology. The most likely or larger, broken off, coherent masses of pure gypsum/anhydrite explanation for the coarsely crystalline halite is that the smaller from the Bandarkas Gypsum Member that were included within crystalline grains preserving distinct thrust-related deformation the Sahwal Marl during deformation. textures have been locally recrystallised by fluid-assisted dissolu- The brittle–ductile deformation preserved in the gypsum-marl tion/reprecipitation during the early stages of telogenesis, result- lithologies of the road-cuts contrasts with the near exclusive duc- ing in coarsely crystalline halite. As this coarsely-crystalline tile fabrics seen in the halite within the mine. In the near surface halite precipitated during early entry into the telogenetic realm (in the mine), the halite is relatively rheologically strong, when it shows no relationship to the deformation fabrics preserved in compared to the potassic salts in the mine. The halite succession the adjacent unaltered halites. is also much more coherent than the adjacent friable gypsum marl, The differences in deformation style we observe between the which is acting as a relative aquifer compared to the two cross sections contrasts with the current perception and mod- halite-dominant section that is acting as a relative aquitard as it elling practice that evaporites act as homogeneous, ductile, mobile dissolves mostly from its edges inward (Warren, 2006). layers (e.g. Chapple, 1978; Jackson and Talbot, 1986; Vendeville When acting as a detachment at depth, though, the weaker unit and Jackson, 1992; Morley and Guerin, 1996; Rowan et al., 2004; is the halite due to its great propensity to flow under even minor Rowan and Vendeville, 2006; Dirkzwager and Dooley, 2008). The burial conditions (Warren, 2006). On a relative scale the rheology ductile deformation observed within the Khewra Mine of both halite and the gypsum marl are orders of magnitude cross-section is as expected for a detachment in rock-salt; how- weaker than the sedimentary rocks above (Urai et al., 2008). As ever, the local heterogeneity of the potash marl layers exhibit a such the red gypsum marl would still have acted as a rheologically rheological change between the lithologies allowing for the forma- weak horizon, much like the halite unit, though it has responded to tion of halite boudin-like zones of coarse-crystalline halite. As the deformation and uplift quite differently. The presence of these fab- halite-bearing zone and the adjacent gypsiferous marls are uplifted rics gives a good indication that the entire Salt Range Formation to the surface, all halite is leached from the detachment and only was accommodating the deformation of the overlying strata. gypsum remains to indicate the former halite-lubricated thrust zone. The loss of halite volume in the at-surface thrust zone creates 5.2. Meso- and micro-scale deformation further karstic accommodation space where veins of satin-spar gypsum grow in the various marls, with brittle conjugate orienta- Halite crystals in the mine show two endmember styles (i) tions tied to halite loss (Gustavson et al., 1994; Moragas et al., medium-crystalline clear grains showing sub-rounded sutured 2013). edges, with local zones of biaxial elongation and (ii) Thus, we see a transition from purely ductile deformation to the coarse-grained halite crystals with edge selvages defined by clay incorporation of more brittle features. The change of deformation and gypsum plates, and no obvious preferred growth directions style is more prominently exposed in the brittle gypsum catacla- (Fig. 10A, C, and E). This dichotomy is not unexpected as halite is sites and blocks of microspar gypsum observed in the Khewra known to readily recrystallise through grain boundary migration Road cross-section. Though both ductile deformation, in the form in the presence of brine fluids (Schenk and Urai, 2004) and to recrys- of S–C fabrics and gypsum slivers, and brittle deformation, as dis- tallise in any phreatic environment that oscillates between halite played by the gypsum cataclasites and boudins, are present; the undersaturation and supersaturation (Warren, 2006). The proportions of ductile to brittle deformation are more even. This medium-crystalline halite comprising the majority of the layered indicates that as a whole the detachment is quite varied in its samples at the meso- and micro-scale samples from the mine exhi- response to stress as it is exhumed. The S–C fabrics would not have bits a granular pressured-sutured edge texture that preserves a dis- formed without the presence of significant accumulations of tinct shape fabric (sample SRLR-06, Fig. 10C and D), which stress; thus, their presence indicates all members of the Salt corresponds to the fabric in the hand specimen of sample Range Formation are responsible for accommodating far-field SRLR-06: 62/250. stresses. From this we can draw the conclusion that our current The strong foliation displayed in the Khewra Mine cross-section modelling techniques, while rheologically accurate at larger scales, (Fig. 3) is supported at a grain-scale by the shape fabric preserved do not capture the true complexity we observe in nature where in the texturally-older deformed halite. Samples SRLR-05 and -06 local outcrop scales indicate a combination of regional ductile also show coarsely-crystalline halite crystals that locally appear deformation driven textures and overprinted by tectonic and local to destroy the smaller, deformed crystals. These coarser crystals karst induced brittle responses. L. Richards et al. / Journal of Asian Earth Sciences 113 (2015) 922–934 933

6. Conclusions Pakistan Academy of Sciences for their support and hospitality as well as the Khewra Mine Deputy Manager of mining Mr. Irfam The Salt Range in northern Pakistan is an ideal location for Ahmad and Chief Engineer Mr. Bakhtiar Ali for allowing us access studying an active salt detachment as it presents ample opportu- and sampling within the Khewra Mine. The contributions to this nity for sample collection and detailed structural analysis at both paper by Richards, King and Collins form TRaX Record 302. outcrop and in the subsurface. In our attempt to characterise the detachment at the meso-scale we presented two detailed cross-sections: References

Artieda, O., 2013. Morphology and micro-fabrics of features on gyprock The Khewra Mine cross-section establishes the compositional exposures in a semiarid environment (Ebro Tertiary Basin, NE ). variability present within the Billianwala Salt Member through 196, 198–210. which it was taken. The structures observed illustrate miner- Baker, D.M., Lillie, R.J., Yeats, R.S., Johnson, G.D., Yousuf, M., Zamin, A.S.H., 1988. alogical and rheological differences within a predominantly Development of the Himalayan frontal thrust zone: salt range, Pakistan. Geology 16, 3–7. ductile material. Berthé, D., Choukroune, P., Jegouzo, P., 1979. Orthogneiss, mylonite and non-coaxial The Khewra Road cross-section through the Sahwal Marl deformation of granites: the example of the South Armorican Shear Zone. J. Member shows the Salt Range Formation is not a single unit Struct. Geol. 1, 31–42. Boyer, S.E., Elliott, D., 1982. Thrust systems. AAPG Bull. 66, 1196–1230. but a combination of lithologies which display strain through Burbank, D.W., Beck, R.A., 1989. Early pliocene uplift of the salt range: temporal brittle, ductile and brittle–ductile mechanisms. constraints on thrust wedge development, Northwest Himalaya, Pakistan. Special Pap. Geol. Soc. Am. 232, 113–128. Butler, R.W., Coward, M.P., Harwood, G.M., Knipe, R.J., 1987. Salt control on thrust Both cross-sections show consistent NW dipping bedding and geometry, structural style and gravitational collapse along the Himalayan foliation at 348° and 351° respectively, which mirrors the mountain front in the salt range of northern Pakistan. In: Lerche, I., O’Brien, J.J. large-scale structures of the overriding fold-thrust belt and more (Eds.), Dynamical Geology of Salt and Related Structures. Academic Press Inc., Orlando, FL, pp. 339–418. distal Himalayas. Both intervals also show the influence of near Chapple, W., 1978. Mechanics of thin-skinned fold and thrust belts. Bull. Geol. Soc. surface alteration, these factors must be understood and incorpo- Am. 89, 1189–1198. rated into a structural interpretation. Chen, L., Khan, D.S., 2009. Geomorphometric features and tectonic activities in sub- Himalayan thrust belt, Pakistan, from satellite data. Comput. Geosci., 35 Optical analyses of samples were conducted in order to charac- Cotton, J., 1997, in Compressional Fold and Thrust Belts [Ph.D. thesis]: terise the halite at a micro-scale. Though evidence for grain bound- London, , Imperial College of Science and Technology, p. 318. ary migration and lattice distortions were identified, the significant Cotton, J., Koyi, H., 2000. Modeling of thrust fronts above ductile and frictional recrystallisation observed throughout, hinders our ability to sub- detachments: application to structures in the salt range and potwar plateau, Pakistan. Geol. Soc. Am. 112, 351–363. stantiate a relation between the micro-scale and meso-scale. Dahlstrom, C.D.A., 1969. Balanced cross sections. Can. J. Earth Sci. 6, 743–757. As no direct correlation between the meso-scale and Dahlstrom, C.D.A., 1990. Geometric constraints derived from the law of micro-scale structures was made it is impossible to state whether conservation of volume and applied to evolutionary models for detachment folding. AAPG Bull. 74, 336–344. the specific microstructures observed here can be linked to Davis, D.M., Lillie, R.J., 1994. Changing mechanical response during continental larger-scale fold-thrust belt geometry. A large volume of research collision: active examples from the foreland thrust belts of Pakistan. J. Struct. has been undertaken to understand the flow and transport proper- Geol. 16, 21–34. Davis, D.M., Suppe, J., Dahlen, F.A., 1983. Mechanics of fold-and-thrust belts and ties of salt (Jackson and Talbot, 1986; Urai et al., 1987, 2008). As accretionary wedges. J. Geophys. Res. 88, 1153–1172. such our predictions of the relationships between meso- and Desbois, G., Závada, P., Schléder, Z., Urai, J., 2010. Deformation and recrystallization micro-scale structures are reasonable, since it is well established mechanisms in actively extruding salt fountain: microstructural evidence for a switch in deformation mechanisms with increased availability of meteoric that microstructures are recorded within halite grains when the water and decreased grain size (Qum Kuh, central ). J. Struct. Geol., 32 correct criteria are met (Urai et al., 1987, 2008; Warren, 2006). Dirkzwager, J.B., Dooley, T.P., 2008. In-situ stress modeling of a salt-based gravity Further research in this area should include many more samples driven thrust belt in a passive margins setting using physical and numerical modeling. Am. Rock Mech. Assoc. for analysis and samples located below the active phreatic zone Duroy, Y., Farah, A., Lillie, R.J., 1989. Subsurface densities and lithospheric flexure of in order to reduce or eliminate the recrystallisation damage to the Himalayan foreland in Pakistan. Special Pap. Geol. Soc. Am. 232, 217–236. the deformed microstructures. Well core samples are perfect can- Gee, E.R., 1980, Pakistan geological Salt Range Series: Directorate of Overseas didates, though the number of wells drilled into salt detachments Surveys, United Kingdom, for the , and Geological Survey of Pakistan, 6 sheets, scale 1:50,000. of actively deforming fold-thrust belts is exceedingly small. Gee, E.R., 1989. Overview of the geology and structure of the Salt Range, with Much work has been undertaken studying the mechanical prop- observations on related areas of northern Pakistan. Special Pap. Geol. Soc. Am. erties of halite (Urai et al., 1986, 1987; Schléder and Urai, 2005; 232, 95–112. Ghazi, S., Mountney, N.P., Butt, A.A., Sharif, S., 2012. Stratigraphic and Desbois et al., 2010). The composition of the Salt Range detach- palaeoenvironmental framework of the Early Permian sequence in the Salt ment involves significantly more evaporite minerals than just Range, Pakistan. J. Earth Syst. Sci., 121 halite, and probably reflects the more general case that the appli- Grelaud, S., Sassi, W., de Lamotte, D.F., Jaswal, T., Roure, F., 2002. Kinematics of eastern Salt Range and South Potwar Basin (Pakistan): a new scenario. Mar. cation of halite rheology to the mechanical properties to detach- Petrol. Geol. 19, 1127–1139. ments in general is somewhat inaccurate. Further study in this Gustavson, T.C., Hovorka, S.D., Dutton, A.R., 1994. Origin of satin spar veins in region is required to determine whether a significant difference evaporite basins. J. Sedimentary Res. Sect. A: Sedimentary Petrol. Processes 64, 88–94. in large-scale deformation is produced as a result of this detach- Hansberry, R.L., King, R.C., Collins, A.S., Morley, C., 2014. Complex structure of an ment compositional heterogeneity and whether the more brittle exposed shale detachment zone: Khao Khwang fold and thrust belt, central evaporites accommodate deformation or if the primary halite layer Thailand. J. Struct. Geol. (Rev.). Holliday, D.W., 1970. The of secondary gypsum rocks; a review. J. forms a singular major slip horizon. Sedimentary Petrol. 40, 734–744. Jackson, M.P.A., Talbot, C.J., 1986. External shapes, strain rates, and dynamics of salt structures. Geol. Soc. Am. Bull. 97, 305–323. Acknowledgements Jaswal, T.M., Lillie, R.J., Lawrence, R.D., 1997. Structure and evolution of the northern Potwar deformed zone, Pakistan. Am. Assoc. Petrol. Geol. Bull. 81, 308–328. Jaumé, S.C., Lillie, R.J., 1988. Mechanics of the salt-range potwar plateau, Pakistan: a This work was funded by the Australian Research Council grant fold and thrust belt underlain by evaporites. Tectonics 7, 57–71. #DP120101560. ASC is funded by ARC future fellowship Khan, M.A., Ahmed, R., Raza, H.A., Kemal, A., 1986. Geology of petroleum in Kohat- Potwar depression, Pakistan. AAPG Bull. 70, 396–414. #FT120100340. The authors would like to thank the National King, R.C., Backé, G., 2010. A balanced 2D structural model of the hammerhead Centre of Excellence in Geology, University of Peshawar and the delta–deepwater fold-thrust belt, bight basin, Australia. Aust. J. Earth Sci., 57 934 L. Richards et al. / Journal of Asian Earth Sciences 113 (2015) 922–934

King, R.C., Backé, G., Morley, C.K., Hillis, R.R., Tingay, M.R.P., 2010. Balancing and conservation of fossil sites worldwide, Carnets de Géologie/Notebooks on deformation in NW Borneo: quantifying plate-scale vs gravitational tectonics in Geology, Brest, Book, Chapter 6. a delta and deepwater fold-thrust belt system. Mar. Petrol. Geol. 27, 238–246. Satyabala, S.P., Zhaohui, Y., Roger, B., 2012. Stick-slip advance of the Kohat Plateau Kovalevych, V.M., Marshall, T., Peryt, T.M., Petrychenko, O.Y., Zhukova, S.A., 2006. in Pakistan. Nat. Geosci., 5 Chemical composition of seawater in Neoproterozoic: results of fluid inclusion Schenk, O., Urai, J.L., 2004. Microstructural evolution and grain boundary structure study of halite from salt range (Pakistan) and Amadeus Basin (Australia). during static recrystallization in synthetic polycrystals of Precambrian Res., 144 containing saturated brine. Contrib. Mineral. Petrol., 146 Koyi, H.A., Vendeville, B.C., 2003. The effect of décollement dip on geometry and Schléder, Z., Urai, J.L., 2005. Microstructural evolution of deformation-modified kinematics of model accretionary wedges. J. Struct. Geol. 25, 1145–1450. primary halite from the Middle Triassic Röt Formation at Hengelo, The Krishnan, M., 1966. Salt tectonics in the Punjab salt range, Pakistan. Geol. Soc. Am. . Int. J. Earth Sci. (Geol. Rundsch.), 94. Bull. 77, 115–122. Simpson, G.D.H., 2010. Influence of the mechanical behaviour of brittle–ductile Leathers, M., 1987, Balanced Structural Cross Section of the Western Salt Range and fold-thrust belts on the development of foreland basins. Basin Res. 22, 139–156. Potwar Plateau, Pakistan: Deformation Near the Strike-Slip Terminus of an Singh, S.P., Singh, B.P., 2010. Geothermal evolution of the evaporite-bearing Overthrust Sheet, M.S. thesis, Oregon State Univ., Corvallis, p. 279. sequences of the Lesser Himalaya, India. Int. J. Earth Sci. 99, 101–108. Lillie, R.J., Yousuf, M., 1986. Modern analogs for some midcrustal reflections Smith, A.G., 2012. A Review of the Ediacaran to Early Cambrian (Infra-Cambrian) observed beneath collisional mountain belts. In: Barazangui, M., Brown, L., Evaporates and Associated Sediments of the Middle East: Geological Society, (Eds.), Reflection seismology: The Continental crust, American Geophysical London, Special Publications, vol. 366, pp. 229–250. Union, Geodynamics Series, vol. 14, pp. 55–65. Suppe, J., 2007. Absolute fault and crustal strength from wedge tapers. Geology 35, Lillie, R.J., Johnson, G.D., Yousuf, M., Zamin, A.S.H., Yeats, R.S., 1987. Structural 1127–1130. development within the Himalayan foreland fold-and-thrust belt of Pakistan. Urai, J.L., Spiers, C.J., Peach, C.J., Zwart, H.J., 1985. A laboratory investigation into the In: Beaumont, C., Tankard, A.J. (Eds.), Sedimentary Basins and Basin Forming interaction of recrystallization and radiation damage effects in polycrystalline Mechanisms, vol. 12. Memoirs of the Canadian Society of Petroleum Geologists, salt rocks. HPT Laboratorium, Insititut voor Aardweten- schappen, University of pp. 379–392. Utrecht, The Netherlands. Moragas, M., Martínez, C., Baqués, V., Playà, E., Travé, A., Alías, G., Cantarero, I., 2013. Urai, J.L., Spiers, C.J., Zwart, H.J., Lister, G.S., 1986. Weakening of rocksalt by water Diagenetic evolution of a fractured evaporite deposit (Vilobí Gypsum Unit, during long term creep. Nature 324, 554–557. Miocene, NE Spain). Geofluids 13, 180–193. Urai, J.L., Spiers, C.J., Peach, C.J., Franssen, R.C.M.W., Liezenberg, J.L., 1987. Morley, C.K., Guerin, G., 1996. Comparison of gravity-driven deformation styles and Deformation mechanisms operating in naturally deformed halite rocks as behaviour associated with mobile shales and salt. Tectonics 15, 1154–1170. deduced from microstructural investigations. Geol. Mijnbouw 66, 165–176. Morley, C.K., King, R., Hillis, R.R., Tingay, M., Backé, G., 2011b. Deepwater fold and Urai, J.L., Schléder, Z., Spiers, C., Kukla, P., 2008. Flow and transport properties of salt thrust belt classification, tectonics, structure and hydrocarbon prospectivity: a rocks. In: Littke, R., Bayer, U., Gajewski, D., Nelskamp, S. (Eds.), Dynamics of review. Earth Sci. Rev. 104, 41–91. Complex Intracontinental Basins: The Central European Basin System. Springer- Park, Y., Means, W.D., 1996. Direct observation of deformation processes in crystal Verlag, Berlin-Heidelberg, pp. 277–290. mushes. J. Struct. Geol. 18, 847–858. Vendeville, B.C., Jackson, M.P.A., 1992. The rise of during thin-skinned Rowan, M.G., Vendeville, B.C., 2006. Foldbelts with early salt withdrawal and extension. Mar. Petrol. Geol. 9, 331–354. diapirism: physical model and examples from the northern and Warren, J.K., 2006, Evaporites: Sediments, Resources and Hydrocarbons. Springer, the Flinders Ranges, Australia. Mar. Petrol. Geol. 23, 871–891. 3300 AA Dordrecht, The Netherlands. Rowan, M.G., Peel, F.J., Vendeville, B.C., 2004. Gravity-driven fold belts on passive Yeats, R.S., Lawrence, R.D., 1984. Tectonics of the Himalayan thrust belt in northern margins. In: McClay, K.R. (Ed.), and Hydrocarbons Systems, vol. Pakistan. In: Haq, B.U., Milliman, J.D. (Eds.), Marine Geology and Oceanography of 82. American Association of Petroleum Geologists Memoir, pp. 157–182. Arabian Sea and Coastal Pakistan. Von Nostrand Reinhold, , pp. 177–198. Sameeni S.J., 2009. The Salt Range: Pakistan’s unique field museum of geology and Yeats, R.S., Khan, S., Akhtar, M., 1984. Late quaternary deformation of the salt range paleontology, In: Lipps J.H. & Granier B.R.C. (Eds.), PaleoParks - The protection of Pakistan. Geol. Soc. Am. Bull., 95.